The Wendella glides beneath the Michigan Avenue Bridge, headed toward the lake. From where I stand on the top deck, we seem to be moving without a peep. The curve of the bridge's shadow passes across the boat, which is studded with people from elsewhere, everyone gaping upward; then the shadow unfolds, curling along the length of the 90-foot deck, down the stern, back across the water. The passengers shield their eyes from the sudden glare. This picture repeats every few minutes here, if not on a Wendella boat than on a boat from another local tour line, Shoreline, Seadog or Chicago Line. Only the chipperness of the tour guide and shine of the sun vary. Indeed, this day, the Wendella moves so smoothly that as it passes the Mercury boats, Wendella's most persistent competition, on the south bank of the river, I can't help notice Bob Borgstrom looking north. I doubt it's unintentional.

Borgstrom, 76, is CEO of Wendella; he is a brusque but cheerful, no-nonsense guy whose tan hints at a life well lived and whose youthful looks suggest a man in his late 50s. His father started Wendella Boats 75 years ago this summer. Which means, more or less, Wendella often being synonymous with sightseeing boats in Chicago, his father started the tour boat business here. That said, Mercury also started 75 summers ago, though at the beginning it offered speedboat tours. Borgstrom acknowledges this shared anniversary, but with agitation, partly because his father, Albert Borgstrom, and Art Agra, who started Mercury, were initially business partners. They were both immigrants — Albert Borgstrom a Swede, 6 feet 4 inches tall, and Agra from Portugal, much shorter.

They did not get along.

Borgstrom relates a bit of this, then quiets and listens to the tour guide, whose voice over the speakers is loud and breezy. We had settled on Wendella's most popular tour, the classic lake and river cruise, 90 minutes long. Without question, it's boilerplate Chicago tourism stuff — our river runs backward, the origin of "Windy City" and so forth — but the ride is pleasant and, as Borgstrom says, you'd be amazed how many locals have never heard these stories.

We launched from the old Wendella dock at the base of the Wrigley Building, headed down the south branch of the river, whipping around at Jackson and doubling back to the lake, the guide tossing random cultural facts, not reading from a script but sounding so clear and brisk, he's not winging it, either. "It's been said that you can be driven wacky driving Wacker!" he says, making a canned joke sound more canned. Even the guy across from me rolls his eyes.

Another thing that hasn't changed: A nagging (if, these days, friendlier) annoyance between rivals.

When Mercury heard I was doing a story on Wendella's 75th, they groaned that Wendella gets all the attention. When Borgstrom heard I was talking to Mercury, he couldn't resist groaning that 75 years ago Wendella was alone in offering narrated tours of the Chicago River, which is correct.

"See, my father bought his tour boat, the first Wendella, from one of Al Capone's old attorneys," he said. "He did repair work for the guy, then the guy sold it to him. But he needed to do more repair work (before it became a tour boat). So he needed financial help. He went to Art, who was at Navy Pier running speedboats then. Art helped him out. They partnered. But, you know, the usual, they start arguing. So my father says he'll go to Michigan Avenue but says, 'Art, stay at Navy Pier.' They part ways. Next season, Art is across the river from him with his boats! Reneging on the agreement."

He continues, Navy Pier gliding past: "Look, my dad was an enterprising guy. He had a ton of patents going. Like pumps for boats and stuff like that. He was a good guy. A giant, cheap Swede. Just physically big. He would tower over everyone. He would shake your hand and put you on your knees he was so strong. Slap your back — I still have those bruises. And he was a carpenter. If we had a boat to finish, he would be out here, morning until late at night, finishing it."

Did you know Art Agra?

"Yeah, very well."

What was he like?

"He was a schmuck. What else you want to know?"

A life on the river

Bob Agra, 52, in naval whites and cargo shorts, rests his hands on the wheel of the Skyline Princess and stares across the river. The boat holds 105 passengers. It's one of six boats in the Mercury fleet; Wendella has nine. (Both are dwarfed by Shoreline, which operates 19.) Agra has a few minutes before the next tour shoves off. He's a quiet guy, the grandson of Art Agra. He took over the company from his father in 1976, though he still captains many of its tour boats. In fact, he drives almost daily. His wife, Holly, sells the tickets. Helming a boat, she says, "remains his favorite part of this business, I think." It's a weekday morning. I ask Agra if he always planned to be part of the family tour boats. He takes a long time before answering.

"I was supposed to be the first Agra to go to college," he says finally. "I was going to get a degree, lead a normal life, not a life on the river. Things didn't work out like that. Looking back, though, I'm glad I got thrust into it. But then? Well, my dad was a heavy smoker and fell into ill health. I was working here as a summer job when he died (of a heart attack). I was only 18 and I was the only child. Then I was running Mercury. You play the hand you're dealt."

He was running the company with his mother, who died five years later, Holly said. She and Bob were married at 20 years old. "It was very hard," she remembers. "He did not have many trained captains, but he had no choice. Bob had been trained as a captain but his father never offered him training in how to run a business. But what are you going to do? This was the only source of income for him and his mother. It was a much simpler business then — a lot of people still lacked air conditioning, and tourism wasn't what it is now, so a lot of people really just wanted to ride the boat to cool off in the summer."

I ask Bob Agra if he remembered Art, his grandfather.

Another long pause. "Oh, I guess he was kind of … excitable. He was a classic maritime personality," he says, and then, commenting on the split between Art and Albert, a conflict everyone involved with Mercury now is too young to remember firsthand, "I would suppose they would both liked to have been in charge."

Before we met, I was a passenger on his Wacky Pirate Cruise, which is every weekend and, if not so wacky, definitely about pirates. The boat moves very slowly. Two crew members, Buccaneer Bob (not Agra) and a guy in pigtails and duct-taped glasses playing an archetypal nerd, greet you. They begin with a little pirate history, then lead the passengers in a treasure hunt — basically the same standard tour boat-delivered Chicago history, but doled out using clues.

Buccaneer Bob, in pirate boots and hat, tells bad jokes, ribs the children and gives everyone a pirate name; then, an hour later, it's over. It's a cute tour, a sweet, charming hour — not as engaging as the Wendella Lake and River Tour, but not intended for adults, either. The kids parade up and down the deck led by Buccaneer Bob and scream their best "Arghhhhh!" and before it's over Buccaneer Bob announces that each, "through the power invested in me by King Richard Daley the Second," has become an honorary pirate, a scoundrel of the seas or, at the least, a rowdy rogue, doomed to the Chicago River.

Years of competition

The Wendella passes Union Station, then makes a hard U-turn in the river. "What I'm going to tell you," Borgstrom says, "you're not going to print anyway." He then tells me of decades of skirmishes between Wendella and Mercury, fighting that sounds less like a healthy rivalry than a gang war. Agra, asked about these skirmishes, sighs and smiles warily. Holly also sighs. They both say they've heard this stuff all their lives but lack specifics.

Not Bob Borgstrom, though, who started at Wendella as a barker on Michigan Avenue — when the city still let tour operators hire essentially carnival barkers to boisterously cajole passersby into taking a boat ride. He remembers rivals stealing Wendella boats and crashing them; he remembers fistfights between crews; he remembers people threatened with guns and the story of a Wendella barker "at night, after the last boat left the dock, standing alone," getting jumped, tied to a flagpole and beaten. He remembers his father holding Art Agra by the throat, dangling him over the river.

Score one for Wendella.

That said, during World War II, he also remembers the military arriving unannounced and ordering the passengers off the Wendella and confiscating the boat, for use in naval exercises. "That almost killed my old man," he says. The Mercury boats, however, were all a bit smaller than the Wendella boats, Agra explains, and therefore less use to the Navy, which wanted boats 60 feet or longer. Mercury spent the war untouched.

Score one for Mercury.

Friends and neighbors

Ironically, 75 years later, Mercury and Wendella complement each other better than they did when they had business together. Wendella runs the Chicago Water Taxi; Mercury has the Chicago Architecture Foundation's popular river tours. Wendella offers a classic sightseeing experience; Mercury has a knack with cleverness, ghost tours, tours for people and dogs, "created after 9/11," Holly said, "when we weren't sure Chicago would get visitors."

"See, with each generation, the fights died down and business mellowed," Agra said. "At some point, we forgot what they'd been fighting about. It was in everyone's interest to get along." Albert Borgstrom died in 1977, a year after Art Agra. The tours shifted from history and trivia to focusing, in the '80s, on architecture; within the last decade alone, as tourism skyrocketed, both lines added more boats than either had in the previous decades combined.

Bob Agra has two sons, one about to enter law school and one who works for Lettuce Entertain You. He doesn't know if they will take over after him. Wendella, meanwhile, is run primarily by Bob Borgstrom's sons, Steve and Mike, who is president.

"From what I hear, it really was the Wild West on the river," says Mike. "But when Bob (Agra) and I got involved, cooperation began. Bob and Holly were guests at my wedding. We consider ourselves neighbors, all these years later, and with a neighbor, you have it in the back of your head that you might need to borrow their lawnmower once in a while."